1. Field of the Invention
The present invention relates generally to liquid crystal display panels, and more specifically to a lighting apparatus used for illuminating an LCD panel from behind.
2. Description of the Related Art
Lighting apparatus for backwardly illuminating LCD panels are known in the art as shown and described in Japanese Patent Publication (Kokai) 91-5726. The lighting apparatus consists of a light guide panel and a light source for injecting light horizontally into the light guide from one edge of the panel. The lower surface of the light guide is formed with such a pattern of dots that it irregularly reflects the light. The density of the dots is varied with distance from the entry edge of the light guide so that the LCD panel is illuminated uniformly. However, the LCD panel, when illuminated uniformly, exhibits inherent asymmetric contrast ratios (between white dots and black dots) as the vertical viewing angle varies as shown in FIG. 1A, although the contrast ratios with respect to the horizontal viewing angle are substantially symmetrical as shown in FIG. 1B. As a result, when the LCD panel is viewed by an operator from a normal working position, the lower portion of the panel has an unsatisfactory low brightness and contrast in comparison with those of the upper portion of the panel.